Wired says Apple and AT&T are in a loveless marriage. There are great mutual benefits to the relationship, but overall both companies are frustrated with each other.

Apple hates AT&T for its crappy network, and its limitations on customers. AT&T hates Apple for being a bunch of newbies when it comes to the phone business. For instance:

One of the iPhone’s problems was that Apple had chosen to source the radio from Infineon, whose hardware was used widely in Europe but rarely in the US, where cell towers are placed farther apart and reception was therefore less forgiving. AT&T would say “Let’s resolve these issues together” and Apple would say “No, you resolve them. They’re not our problem. They’re your problem.” (Via: ZDnet)

In addition to technical problems, there were cultural problems. An AT&T rep asked Steve Jobs to wear a suit to meet with AT&T's board. One of Steve's deputies responded*: "We’re Apple. We don’t wear suits. We don’t even own suits."

The problems between the two companies are about to enter a new phase, as Wired says Apple is now working on a chip with Qualcomm that will allow the iPhone to operate on both AT&T and Verizon.